Data from: Potential age differences in the migratory behaviour of a nocturnal songbird migrant during autumn and spring

In migratory songbirds, older individuals are thought to be more efficient migrants than younger individuals. Age-specific differences in migratory efficiency have been reported mainly in respect of arrival timing, energy stores, rate of energy accumulation, departure behaviour, and departure direction. Yet, these traits were rarely assessed simultaneously in a single species. We further lack information whether age-specific differences in behavioural traits present in autumn still manifest to the same degree in spring. Here we used the northern wheatear (Oenanthe oenanthe), a long-distance nocturnal songbird migrant, and investigated age-specific differences in energy stores at capture (autumn: 1059 birds/spring: 803 birds), rate of energy accumulation (168/147), nocturnal departure timing (126/105), and departure direction (94/77) for both seasons. We found that in autumn, young northern wheatears departed significantly later in the night than older birds. This difference was not observed in spring. The resulting advance in nocturnal departure timing by young birds from autumn to spring may be due to learning based on experience gained during autumn, and/or to selective disappearance of those young individuals showing late departure times during autumn. We found no age-specific difference in any of the other migratory traits investigated. To get a better understanding of age effects in songbird migrants, we need to study the potential adjustments of migratory behaviour within the individual over its life time. By individually tracking songbirds throughout their lifetime, we could start estimating whether a certain migratory decision (fuelling, departure, orientation) translates into higher (or lower) fitness, and whether individuals adjust their migratory behaviour based on learning from “wrong decisions”.

在迁徙鸣禽中，学界普遍认为年长个体的迁徙效率高于年幼个体。此前针对迁徙效率的年龄特异性差异的研究，主要集中在到达时间、能量储备、能量积累速率、离巢行为以及离巢方向这几个方面。然而，鲜有研究在同一物种中同时评估这些性状。此外，我们仍不清楚，秋季存在的行为性状年龄特异性差异，在春季是否仍会以同等程度显现。本研究以长距离夜行性迁徙鸣禽北鵖（Oenanthe oenanthe）为研究对象，调查了两个季节（秋季：1059只/春季：803只）捕获个体的能量储备、能量积累速率（样本量分别为168/147）、夜间离巢时间（样本量126/105）以及离巢方向（样本量94/77）的年龄特异性差异。研究结果显示，秋季时北鵖幼体的夜间离巢时间显著晚于成体，但这一差异在春季并未出现。幼体个体从秋季到春季夜间离巢时间的提前，可能源于其在秋季积累的经验带来的学习行为，亦或是秋季离巢较晚的幼体个体发生了选择性消失。其余所调查的迁徙性状均未发现年龄特异性差异。为更深入地理解迁徙鸣禽的年龄效应，我们需要研究个体在其一生中迁徙行为的潜在调整。通过对鸣禽个体进行终生追踪，我们将能够评估特定迁徙决策（能量补给、离巢行为、定向导航）是否会带来适合度的升降，以及个体是否会基于对"错误决策"的学习来调整其迁徙行为。